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Submitted to: American Meteorological Society Proceedings
Publication Type: Proceedings Publication Acceptance Date: 10/28/2002 Publication Date: 10/28/2002 Citation: NORTHUP, B.K., SCHNEIDER, J.M., DANIEL, J.A. 2002. THE EFFECTS OF MANAGEMENT AND PRECIPITATION ON FORAGE COMPOSITION OF A SOUTHERN TALLGRASS PRAIRIE. Available from: http://ams.confex.com/ams/15BioAero/techprogram/paper_49656.htm Proceedings of the American Meterological Society 15th Conference on Biometereology/aerobiology. Interpretive Summary: Tallgrass prairie is used by livestock producers of the Southern Great Plains for putting summer weight gain on yearling cattle. Forage composition is an important indicator of condition of these plant communities. The Southern Great Plains has many stressors that cause changes in community composition (and condition), and sustainable management requires an understanding of their effects. We examined how pasture management and quarterly precipitation affected the contribution of 4 key species groups to total production during 1984-1995, and whether current forecast models were accurate enough to be used as tools in grazing management. Both management and precipitation pattern (quarterly and annual) affected the plant community, with the most negative effects noted under either heavy grazing or no management (no grazing, haying, etc.). Cycles in production by the different forage groups occurred during the study, but the most significant changes occurred in 1988-1990 due to low precipitation in October 1988-April 1989. Timing of precipitation affected composition of the forage produced, and responses were likely related to growth habits of the different plant species. Production by the dominant warm-season grasses was related to high precipitation in October-March, while April-June rainfall was related to production by shallow-rooted annual bromes (cheatgrass). July-September rainfall was positively related to short-lived broadleaf plants (summer forbs), and production by weedy warm-season grasses (mostly annuals) was related to low precipitation in January-June. These relationships indicate that quarterly precipitation forecasts could be a useful management tool. However, current models are most accurate for strong El Nino (high rainfall) events. If forecasting tools can be improved so they better predict dry periods, they could help define potential changes in plant communities and improve management of tallgrass prairie. Technical Abstract: Forage composition is an important part of grassland productivity in the Southern Great Plains. Both paddock management and climate can affect, either positively or negatively, community composition. Measures of 3-month total precipitation might serve as a useful tool for fine-tuning grazing management. This study described how different grazing pressures and precipitation patterns affected forage composition of 1.6 ha pastures on a southern tallgrass prairie site during 1984-1995. Forage composition (% of total forage produced) of four groups of plants was defined annually; the dominant warm-season grasses ('Big 4'), weedy warm-season grasses (8 species), annual bromes (2 species), and broadleaved forbs (23 species). Temporal changes in composition were examined, and Spearman's correlations were used to determine if composition was related to recorded annual and quarterly precipitation. The accuracy of 3-month forecasts of precipitation (1995-2000) was also determined. Composition of all paddocks changed in 1988-89 and persisted till 1995. The 'Big 4' grasses declined and invasive warm-season grasses, forbs, and annual bromes increased. Changes coincided with drought periods in 1988-89 that interacted with management to cause pasture differences. Significant (P<0.10) correlations were noted between 'Big 4' grasses, forbs, and weedy warm-season grasses, and yearly or 'seasonal' (Oct-Sept) precipitation, as were relationships for shorter time intervals. On a quarterly basis, positive correlations were noted between 'Big 4' grasses and 1st and 4th quarter precipitation, annual bromes and 2nd quarter rainfalls, and forbs and 3rd quarter rainfalls. Experimental 3-month forecasts were moderately accurate at defining some high precipitation events (1997-98), but were unsuccessful with dry periods. If improved, 3-month forecasts could be a useful support tool for the tactical management of tallgrass prairie. |
